Skip to content
Allin
Sign up · Sign in

Weight-based medication dosage calculator

Turns a weight-based prescription into a concrete amount: from body weight, the dose in mg per kg and — for a liquid — the concentration in mg per ml, it works out the milligrams and millilitres per dose and the total per day. An arithmetic aid only, never a substitute for a clinician.

Related tools

All Medical & clinical tools →
Body surface area calculatorCompute your body surface area (BSA) with the five published formulas — Mosteller, Du Bois, Haycock, Gehan & George and Boyd — side by side.Ideal weight calculatorEstimate your ideal body weight (Devine formula).Target weight for a BMI calculatorFind the body weight that matches a target BMI for your height.BMR calculatorEstimate your Basal Metabolic Rate (Mifflin-St Jeor).Blood alcohol calculatorEstimate your blood alcohol concentration (BAC) with the Widmark formula.Pregnancy Weight Gain CalculatorRecommended pregnancy weight gain by pre-pregnancy BMI (IOM), with the expected gain at your current week.Weekly weight-loss from calorie deficitConvert a daily calorie deficit into expected weekly and monthly weight loss.Pack-years calculatorCompute your smoking pack-years from packs per day and years smoked.

The Weight-based medication dosage calculator turns Body weight, Dose (mg per kg per dose), Doses per day, Liquid concentration (mg per ml, 0 = tablet) into Per dose, Per dose (liquid), Total per day, instantly and for free. For instance, with Body weight = 20 kg, Dose (mg per kg per dose) = 15, Doses per day = 3 and Liquid concentration (mg per ml, 0 = tablet) = 100 it returns Per dose = 300 mg, Per dose (liquid) = 3 ml and Total per day = 900 mg.

How to use it

  1. Enter your values: Body weight, Dose (mg per kg per dose), Doses per day, Liquid concentration (mg per ml, 0 = tablet).
  2. Read the result instantly: Per dose, Per dose (liquid), Total per day.

Frequently asked questions

How does the Weight-based medication dosage calculator work?

It takes Body weight, Dose (mg per kg per dose), Doses per day and Liquid concentration (mg per ml, 0 = tablet) and derives Per dose, Per dose (liquid) and Total per day from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

4 values: Body weight (kg), Dose (mg per kg per dose), Doses per day and Liquid concentration (mg per ml, 0 = tablet). Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Body weight = 20 kg, Dose (mg per kg per dose) = 15, Doses per day = 3 and Liquid concentration (mg per ml, 0 = tablet) = 100, the calculator returns Per dose = 300 mg, Per dose (liquid) = 3 ml and Total per day = 900 mg. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

How much does the result change with different inputs?

It moves a lot. Using Body weight = 22 kg, Dose (mg per kg per dose) = 30, Doses per day = 6 and Liquid concentration (mg per ml, 0 = tablet) = 200 instead, Per dose goes from 300 mg to 660 mg — which is why it is worth testing a few scenarios rather than trusting a single figure.

Which units should I enter the values in?

Enter Body weight kg. Metric and US units are both supported — switch system and the figures convert for you.

What does it give for smaller values?

Scaled down to Body weight = 18 kg, Dose (mg per kg per dose) = 7.5, Doses per day = 2 and Liquid concentration (mg per ml, 0 = tablet) = 50, Per dose comes out at 135 mg. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Checking one clinical number against the definition that gives it meaning: a dose against a body weight, a laboratory value corrected for the albumin or glucose that distorted it, a blood pressure against a guideline's threshold table, a heart rate or a basal metabolic rate against the formula that defines it.

What is the most common mistake?

Reading the output as a finding. Every figure here is arithmetic on numbers you typed: a correction formula measures nothing, and a threshold table classifies one reading rather than a person. Blood pressure in particular means little until it has been measured repeatedly on separate occasions, and a dose worked out here is a way of checking a prescription, never of writing one.

How accurate is it, and what are the limits?

Educational estimate only. Medication dosing must be set and verified by a qualified healthcare professional — never dose from this tool alone.

What is the difference between the Weight-based medication dosage calculator and the Body surface area calculator?

This one returns Per dose and Per dose (liquid); the Body surface area calculator returns Body surface area (m²) and Du Bois (m²). That is the whole difference — open the one whose figure you need.

Further reading

All guides →
ExplainerWeight-Based Dosing, and Where the Arithmetic Goes WrongMilligrams per kilogram is one multiplication, and that is exactly why it fails: the documented errors are unit slips, misplaced decimal points and the wrong body weight, not hard maths. Here is the arithmetic done properly, the three body weights that give three different answers, and what body surface area changes.ExplainerCorrected Sodium, and Why Glucose Moves ItHigh blood glucose pulls water out of cells and dilutes the sodium in it, so a measured sodium in a hyperglycaemic patient reads lower than the real one. Here is the correction, both of the published factors, a case where they disagree by 4 mmol/L, and the different problem that lipids cause.ExplainerCorrected Calcium: Why Albumin Changes the NumberAbout half of blood calcium is bound to albumin and inactive, so a total-calcium result on a low-albumin patient reads low even when the active fraction is normal. Here is the correction in both unit systems, a worked case, and the honest verdict on how badly it performs.ExplainerHow Long Does Alcohol Stay in Your System?The body clears roughly one standard drink per hour. See how long alcohol stays in blood, breath and urine — and why you can't rush it.ExplainerWhat Are Pack-Years?A pack-year sums up a smoking history in one number. Here is how it is calculated and why doctors use it to judge risk and screening.ExplainerWhat Is Your BMR? Basal Metabolic Rate ExplainedYour basal metabolic rate is the energy your body burns at complete rest. Learn how the Mifflin-St Jeor equation estimates it and what raises or lowers it.